Many of today's multi-stage switching networks implement the well-known Clos switching architecture. An example of a Clos network is shown in FIG. 1, wherein the network 100 comprises a plurality of leaf switches 102 and a plurality of spine switches S1-S16. The ports of the leaf switches and the ports of the spine switches are interconnected by a spreader network 104 (also referred to as an interconnect). In the sample network shown in FIG. 1, each leaf switch 102 has sixteen inner ports (ports that are coupled to the spine switches) and sixteen outer ports (ports that can be coupled to external components, such as external computing nodes). Each leaf switch 102 may be implemented as a single switch, or, as shown in FIG. 1, may be implemented using a plurality of interconnected smaller switches (in the example shown, each leaf switch 102 is implemented with eight interconnected 8-port switches). In each leaf switch 102, information may be switched from any port of that leaf switch to any other port of that leaf switch. Similarly, in each spine switch S1-S16, information may be switched from any port of that spine switch to any other port of that spine switch.
Each inner port of a leaf switch 102 is coupled to a separate one of the spine switches S1-S16, as shown. With each leaf switch 102 having sixteen inner ports, and with sixteen spine switches S1-S16, there is a one-to-one relationship between an inner port of a leaf switch 102 and a spine switch. Likewise, each spine switch has eight ports. Each of these ports is coupled to a separate one of the leaf switches 102. With each spine switch having eight ports, and with eight leaf switches 102, there is a one-to-one relationship between a port of a spine switch and a leaf switch 102. Interconnected in this way, each leaf switch 102 may switch information to any one of the spine switches S1-S16. Likewise, each spine switch S1-S16 may switch information to any one of the leaf switches 102.
One of the advantages of a Clos network is that it has the desirable property of supporting full cross sectional bandwidth between all of the interconnected ports. This property ensures that there is sufficient capacity in the network to handle the traffic between all hosts regardless of the traffic pattern. One of the drawbacks of a Clos network, however, is that the complexity of the interconnect 104 can grow very rapidly. Even with the relatively small network shown in FIG. 1, one hundred twenty eight physical links are already required between the inner ports of the leaf switches 102 and the spine switches S1-S16. With a larger network having more switches and ports, the interconnect complexity would grow many fold. In fact, the complexity of the interconnect 104 would grow exponentially with the increase in switches and ports. That being the case, the cost of the interconnect 104 can quickly become a significant portion of the cost of the overall network. In addition, the increased complexity can make the interconnect 104 extremely difficult and costly to implement and manage. In light of these shortcomings, a need exists for an interconnect infrastructure that provides the same connectivity as that provided by the Clos interconnect but yet is simpler in structure and implementation.